On Mon, Feb 27, 2023 at 08:58:37AM -0600, Mario Limonciello wrote:
On 2/27/23 08:55, Guenter Roeck wrote:
On Mon, Feb 20, 2023 at 12:07:28PM -0600, Mario Limonciello wrote:
AMD has issued an advisory indicating that having fTPM enabled in BIOS can cause "stuttering" in the OS. This issue has been fixed in newer versions of the fTPM firmware, but it's up to system designers to decide whether to distribute it.
This issue has existed for a while, but is more prevalent starting with kernel 6.1 because commit b006c439d58db ("hwrng: core - start hwrng kthread also for untrusted sources") started to use the fTPM for hwrng by default. However, all uses of /dev/hwrng result in unacceptable stuttering.
So, simply disable registration of the defective hwrng when detecting these faulty fTPM versions. As this is caused by faulty firmware, it is plausible that such a problem could also be reproduced by other TPM interactions, but this hasn't been shown by any user's testing or reports.
It is hypothesized to be triggered more frequently by the use of the RNG because userspace software will fetch random numbers regularly.
Intentionally continue to register other TPM functionality so that users that rely upon PCR measurements or any storage of data will still have access to it. If it's found later that another TPM functionality is exacerbating this problem a module parameter it can be turned off entirely and a module parameter can be introduced to allow users who rely upon fTPM functionality to turn it on even though this problem is present.
Link: https://www.amd.com/en/support/kb/faq/pa-410 Link: https://bugzilla.kernel.org/show_bug.cgi?id=216989 Link: https://lore.kernel.org/all/20230209153120.261904-1-Jason@zx2c4.com/ Fixes: b006c439d58d ("hwrng: core - start hwrng kthread also for untrusted sources") Cc: stable@vger.kernel.org Cc: Jarkko Sakkinen jarkko@kernel.org Cc: Thorsten Leemhuis regressions@leemhuis.info Cc: James Bottomley James.Bottomley@hansenpartnership.com Co-developed-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Mario Limonciello mario.limonciello@amd.com
v1->v2:
- Minor style from Jarkko's feedback
- Move comment above function
- Explain further in commit message
drivers/char/tpm/tpm-chip.c | 61 ++++++++++++++++++++++++++++++- drivers/char/tpm/tpm.h | 73 +++++++++++++++++++++++++++++++++++++ 2 files changed, 133 insertions(+), 1 deletion(-)
diff --git a/drivers/char/tpm/tpm-chip.c b/drivers/char/tpm/tpm-chip.c index 741d8f3e8fb3..1b066d7a6e21 100644 --- a/drivers/char/tpm/tpm-chip.c +++ b/drivers/char/tpm/tpm-chip.c @@ -512,6 +512,64 @@ static int tpm_add_legacy_sysfs(struct tpm_chip *chip) return 0; } +/*
- Some AMD fTPM versions may cause stutter
- Fixes are available in two series of fTPM firmware:
- 6.x.y.z series: 6.0.18.6 +
- 3.x.y.z series: 3.57.y.5 +
- */
+static bool tpm_amd_is_rng_defective(struct tpm_chip *chip) +{
- u32 val1, val2;
- u64 version;
- int ret;
- if (!(chip->flags & TPM_CHIP_FLAG_TPM2))
return false;- ret = tpm_request_locality(chip);
- if (ret)
return false;- ret = tpm2_get_tpm_pt(chip, TPM2_PT_MANUFACTURER, &val1, NULL);
- if (ret)
goto release;- if (val1 != 0x414D4400U /* AMD */) {
ret = -ENODEV;goto release;- }
- ret = tpm2_get_tpm_pt(chip, TPM2_PT_FIRMWARE_VERSION_1, &val1, NULL);
- if (ret)
goto release;- ret = tpm2_get_tpm_pt(chip, TPM2_PT_FIRMWARE_VERSION_2, &val2, NULL);
- if (ret)
goto release;This goto is unnecessary.
+release:
- tpm_relinquish_locality(chip);
- if (ret)
return false;- version = ((u64)val1 << 32) | val2;
- if ((version >> 48) == 6) {
if (version >= 0x0006000000180006ULL)return false;- } else if ((version >> 48) == 3) {
if (version >= 0x0003005700000005ULL)return false;- } else
return false;checkpatch:
CHECK: braces {} should be used on all arms of this statement #200: FILE: drivers/char/tpm/tpm-chip.c:557:
- if ((version >> 48) == 6) {
[...]
- } else if ((version >> 48) == 3) {
[...]
- } else
[...]
It was requested by Jarko explicitly in v1 to do it this way.
OK, you're right, it is my bad, I'm sorry about that. Send v3 with that feedback reverted.
BR, Jarkko